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Presented at the Twentieth IT3 Conference, May 14-18, 2001, Philadelphia, USA

TREATMENT OF DIFFERENT WASTES BY SUPERCRITICAL WATER OXIDATION
Anders V. Gidner*, Lars B. Stenmark and Kim M. Carlsson
Chematur Engineering AB
Box 430, 691 27 Karlskoga, Sweden
e-mail: a.gidner@chematur.se, Fax: +46 586 642 50
ABSTRACT
If left to conventional treatment processes, the destruction of toxicorganic wastewaters and
associated sludge volume reduction clearly becomes an overwhelming problem. Two options, incineration
and supercritical water oxidation (SCWO), exist for the complete destruction of toxic wastewaters and
organic sludges. Incineration has associated problems such as very high cost and public resentment; on
the other hand SCWO has proved to be a very promising method for thetreatment of many different
wastewaters and sludges.
In early 1998 Chematur Engineering inaugurated its 250 kg/h SCWO demonstration facility and
since then several successful treatability tests have been performed. Among these are tests with different
complex wastes, from a SCWO process point of view. They have been performed in two different ways: 1.
Making the waste treatable in an “ordinary”SCWO unit, i.e. remove halogens and dissolved salts. 2.
Making the SCWO unit able to handle the difficulties in the waste, e.g. halogens.
Another waste, de-inking sludge, has been treated several times. The appealing results from
these tests are that, besides the complete destruction of the organic material, the remaining paper filler
has shown to be good enough for reuse. This exemplifiesthe general possibility to destroy the organic
material in the waste by SCWO and leave a “clean” valuable inorganic material in the effluent, which
could easily be recovered. The extremely clean inorganic material recovered ought to increase the
interest in SCWO treatment. This type of waste may very well be the breakthrough of SCWO.
INTRODUCTION
Oxidation of organic wastes to carbon dioxide,water, and other small molecules can effectively
minimise waste volume and detoxify many hazardous compounds. Incineration in air at atmospheric
pressure is the most common oxidation technique currently practised. However, incineration meets an
increasing opposition from the public and furthermore the cost for incineration of waste has a tendency to
rise constantly because of the increasingdemand on the flue gas cleaning. A supercritical water oxidation
(SCWO) system can handle aqueous streams containing organic material in relatively low concentrations
and offers inherent control over emissions and coupling to energy recovery systems.
Under normal conditions, water is seen in either of its three states: atmospheric steam, liquid
water, or ice. If water is heated and compressed tosufficiently high temperature and pressure a new fluid
state of water emerges. Water at high temperatures and pressures, above 374 °C and 221 bar, is a fluid
that is neither a gas nor a liquid, it is in its supercritical state. The reason for the efficiency of SCWO in
destroying organic compounds is the unique properties of water above its critical point. The change in
magnitude of differentproperties is very rapid at entrance into the supercritical region. Any substance
above its critical point has properties that are in between those of a gas and a liquid. The density of
supercritical water (SCW) is comparable with liquid water densities, and high enough for reasonable
throughputs in a process. On the other hand the viscosity and diffusivity in the supercritical region are
morelike that of a gas. Water gets a high solvating power, because of the low dielectric constant,
obtained when becoming supercritical and most organic compounds and gases are completely miscible in
all proportions in SCW.
In 1995 Chematur Engineering (CEAB) started its SCWO activities by a license agreement for
SCWO signed with Eco Waste Technologies (EWT) and early 1999 Chematur acquired the...
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